Butterfly genome reveals promiscuous exchange of mimicry adaptations among species

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Abstract
Sequencing of the genome of the butterfly Heliconius melpomene shows that closely related Heliconius species exchange protective colour-pattern genes promiscuously. Heliconius butterflies are an excellent system in which to study ecology, behaviour, mimicry and speciation. The genome of the postman butterfly Heliconius melpomene has now been sequenced. Using genomic resequencing of individuals from distinct lineages, the authors document heterogenous patterns of genomic diversity associated with adaptively divergent wing-colour patterns. As the second lepidopteran genome to be sequenced, Heliconius offers novel opportunities for comparative genomics within this economically significant insect order, which includes many pest species, as well as the only domesticated insect, the silkmoth Bombyx mori. The evolutionary importance of hybridization and introgression has long been debated1. Hybrids are usually rare and unfit, but even infrequent hybridization can aid adaptation by transferring beneficial traits between species. Here we use genomic tools to investigate introgression in Heliconius, a rapidly radiating genus of neotropical butterflies widely used in studies of ecology, behaviour, mimicry and speciation2,3,4,5. We sequenced the genome of Heliconius melpomene and compared it with other taxa to investigate chromosomal evolution in Lepidoptera and gene flow among multiple Heliconius species and races. Among 12,669 predicted genes, biologically important expansions of families of chemosensory and Hox genes are particularly noteworthy. Chromosomal organization has remained broadly conserved since the Cretaceous period, when butterflies split from the Bombyx (silkmoth) lineage. Using genomic resequencing, we show hybrid exchange of genes between three co-mimics, Heliconius melpomene, Heliconius timareta and Heliconius elevatus, especially at two genomic regions that control mimicry pattern. We infer that closely related Heliconius species exchange protective colour-pattern genes promiscuously, implying that hybridization has an important role in adaptive radiation.